California Roofing Contractor Exam 2026 (C-39 License) – All-in-One Practice Test to Master Your Certification!

Underlayment provides a protective barrier between the roof deck and the shingles, catching water that gets behind the shingles and offering a smooth surface for proper shingle adhesion. For asphalt shingles, the minimum weight is a single layer of asphalt-saturated felt weighing 15 pounds per 100 square feet. This amount is enough to meet basic protection without extra material. Heavier options, like 30-pound felt or two plies, are not required to meet the minimum, though they may be used in certain conditions or by specific manufacturers. So the single 15-pound underlayment is the correct minimum.